1. Field of the Invention
This invention relates to a mobile communication system, a base station device and a method of estimating a number of uplink packet retransmissions, and particularly relates to a method of estimating a number of uplink packet retransmissions of HSUPA (High-Speed Uplink Packet Access) in the base station device.
2. Description of the Related Art
For a base station device, it is important to measure the radio quality. A method of measuring the radio quality includes a method of measuring the number of NACK (Negative ACKnowledgement) messages to be transmitted and requesting retransmission when an error in received data is serious.
However, it is assumed for the method that a base station device can receive an E-DPCH [E-DCH (Enhanced Dedicated CHannel) Dedicated Physical CHannel]. Because of this, it is not considered for the method that a base station device cannot receive the E-DPCH even if a mobile terminal transmits the E-DPCH.
That is, the radio quality can be measured by measuring an E-DPCH carrying a MAC (Medium Access Control)-e PDU (Protocol Data Unit) transmitted from a mobile terminal by including its retransmission, and comparing the result to the number of MAC-e PDUs received actually. Therefore, it is necessary to measure the number of MAC-e PDUs transmitted from a mobile terminal.
In a mobile communication system as in the above, a method has been proposed of monitoring and grasping a PDU transmission state in a radio link to a mobile terminal for each call, calculating a retransmission occurrence rate as an evaluated value of the radio transmission quality, and determining the radio transmission quality as a deteriorated state if the retransmission occurrence rate is a threshold or more (for example, see patent document 1 (Japanese Patent Laid-Open No. 2003-189368)).
Since the related base station device described in the above cannot measure an E-DPCH that has not been received, it actually grasps the number of retransmissions using an RSN (Retransmission Sequence Number) value indicated to a MAC-e PDU when it receives an E-DPCH.
However, an RSN value can be an error and is finite so that it has the maximum value that can be displayed. Because of this, an RSN value does not always indicate the correct number of retransmissions.
An error rate can be high due to the state of the radio environment when a mobile terminal transmits an E-DPCH. So an E-DPCH cannot be received, or a base station device might not be able to decode a MAC-e PDU accurately even if it receives an E-DPCH.
In the above case, the mobile terminal retransmits the MAC-e PDU in the same process in the next cycle. An HSUPA signal modulating/demodulating device could not know the normal number of retransmissions 1) if it cannot decode the RSN normally and 2) if the maximum allowed times of retransmissions larger than the RSN is set and the RSN is reported as the maximum value to which the RSN can be set. The technique according to the above patent document 1 cannot solve the problem.